January 16, 2014

Do Faster-Growing Old Trees Translate To More Carbon Storage?

by editor

redOrbit Staff & Wire Reports - Your Universe Online

Contrary to the commonly held belief that trees become unproductive as they grow older, new research appearing in the journal Nature demonstrates that most of them experience increases in their growth rates and store more carbon as they age.

As part of their research, the study authors reviewed records from studies on six continents, including measurements from over 650,000 trees belonging to 403 tropical and temperate species. They found that 97 percent of them actually grow more quickly as they advance in age and remove more carbon than expected from the atmosphere.

“Rather than slowing down or ceasing growth and carbon uptake, as we previously assumed, most of the oldest trees in forests around the world actually grow faster, taking up more carbon,” added Smithsonian Tropical Research Institute staff scientist Richard Condit. “A large tree may put on weight equivalent to an entire small tree in a year.”

According to the researchers, rapid growth in giant trees such as the redwood is the rule, not the exception. The largest types of trees can exceed 1,300 pounds (600 kilograms) per year. Their paper also included studies from forests in the Pacific Northwest, measuring growth in trees such as the Douglas fir and the western hemlock.

“In human terms, it is as if our growth just keeps accelerating after adolescence, instead of slowing down. By that measure, humans could weigh half a ton by middle age, and well over a ton at retirement,” lead author Nate L. Stephenson, a research ecologist at the US Geological Survey (USGS) Western Ecological Research Center, said in a statement Wednesday.

The study authors explained that their findings prove that older trees “do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees; at the extreme, a single big tree can add the same amount of carbon to the forest within a year as is contained in an entire mid-sized tree.”

Furthermore, the “apparent paradoxes” of individual tree growth increasing with the tree’s size despite declines in leaf and stand level productivity can be attributed to increases in total leaf area that offset productivity decline and age-related population density reductions. However, they have yet to determine whether or not the accelerated growth rate of individual trees actually increases carbon storage by aging forests.

The study was conducted by a team of 38 scientists from various international research universities, government agencies and non-governmental organizations, including those in the US, the UK, Panama, Australia, Germany, Colombia, Argentina, Thailand, Cameroon, France, China, Taiwan, Malaysia, New Zealand and Spain.